Effect of TiO2 on surface energy characteristics and microstructure of porous alpha-Al2O3 ceramics

The surface free energy components of sintered free standing porous alpha-Al2O3, ceramics doped with varying TiO2 (rutile) content (0-2 wt-% of powder content), and fired at 1300 degrees C and 1400 degrees C have been studied using the capillary rise technique. The liquids used for the wetting experiments were: octane, dodecane, tetradecane, 1-bromonaphthalene, formamide and water. For the ceramics sintered at 1400 degrees C, no spontaneous penetration of the liquids used was observed when the TiO2 content was higher than 0.25 weight-%. Pore size characteristics of the materials were also obtained by carrying out mean flow pore tests. The apparent porosity as well as the mean flow pore size of the sintered compacts decreased with increasing sintering temperature and TiO2 content. The surface energy components i.e. Lewis base (gamma(s)(-)) and the Lifshitz-van der Waals dispersive (gamma(s)(LW)) decreased, and the acid component (gamma(s)(+)) increased for the ceramics as a function of TiO2 content and sintering temperature. No dependence of gamma(s)(LW) on the sintering temperatures studied was observed. The microstructures of the ceramics were investigated by scanning electron microscopy (SEM). The results show an evidence of lattice diffusion of titania at contents below 0.2 wt-%, and of formation of alumina titanate during the sintering process at higher titania contents.